Thermodynamic properties of 55-atom Pt-based nanoalloys: Phase changes and structural effects on the electronic properties.

Atomistic understanding of thermodynamic processes such as phase transitions in nanoalloys is crucial to improve real-life applications of Pt-based nanocatalysts. In this work, we investigate the thermodynamic properties of 55-atom PtCo and PtNi nanoalloys and compare them to reference unary systems, Pt, Co, and Ni. Our results are based on the combination of the parallel tempering Monte Carlo and the revised basin-hopping Monte Carlo algorithms with many-body Gupta potentials, and furthermore, density functional theory calculations were employed to validate the adopted Gupta parameters and to analyze electronic effects induced by structural changes derived from temperature effects. We identified first-order phase transitions for Pt, Co, PtCo, Ni, and PtNi at 727, 1027, 1003, 914, and 1051 K, respectively. Thus, alloying unary Pt nanoclusters with Ni and Co leads to an increase in the melting temperature, indicating that the nanoalloys are able to sustain higher temperatures while maintaining their structure. A low-temperature solid-solid transition was also identified for Pt, which is characterized by a change from a face-centered cubic like structure (putative global minimum configuration) to the icosahedron structure. The structural transformations led by the temperature increase induce small changes on the total density of states, namely, a slight shift of the d-band center toward the highest occupied molecular orbital with increasing temperature, which was found for all considered nanoclusters.